HR: 1330h
AN: H33A-06    [Abstracts]
TI: Assessing Erosion and Deposition from Comparative Analysis of Long Profiles and Probability Distributions of Dune-bed Elevation at the Red Eye Crossing, Mississippi River
AU: * Leclair, S F
EM: leclair@tulane.edu
AF: Department of Earth and Environmental Sciences, Tulane University, Dinwiddie Hall 6823 St Charles ave , New Orleans, LA 70118 United States
AU: Miller, J
EM: jmiller1@tulane.edu
AF: Department of Earth and Environmental Sciences, Tulane University, Dinwiddie Hall 6823 St Charles ave , New Orleans, LA 70118 United States
AB: The probability distribution of dune-bed elevation relative to mean bed level (Ps) is a key element of new river morphodynamic models and the analysis of the range and shape of Ps curves is a powerful tool for assessing dune geometry and the relative sediment-transport conditions at a given time. In addition, spatial analysis of successive bed profiles in the along-stream direction provides a direct estimate of erosion and deposition over time. In order to assess the sediment transport or storage within the lower Mississippi River, we repetitively surveyed a 4-km-long bed profile at a major crossing over a period of about 9 months, recording bed elevations with a 1MHz transducer and high-precision echo sounder. Bed profiles show multi-scale bedforms, and hence we constructed Ps curves for selected stretches showing dunes of similar range of height and length. We also compared our data with those from the USACE recorded at the same site in 2001. Preliminary results show that in most cases, the Ps curves are quite symmetric relative to mean bed level and show a narrow range of values. This is comparable to previous experimental results at relatively low sediment-transport stage and indicates that dune troughs are not eroding the bed downward significantly. Although the mean bed level varies little between surveys, the Ps curves reveal time variation in the proportion of elevations above or below mean bed level, indicating the migration of channel-scale sandwaves, for which sediment flux can be estimated. Future research will include relating Ps curves to vertical sorting and velocity profiles, and comparing sediment-transport rates estimated from theory and acoustic measurements.
DE: 1815 Erosion and sedimentation
DE: 4558 Sediment transport
SC: Hydrology [H]
MN: 2005 Joint Assembly